These studies include detailed analyses of the lipid fatty acid composition of male reproductive tissue in several animals and the metabolism of these lipids. The biosynthesis and interconversion of fatty acids are being studied in testes of animals in vivo and in vitro. Alterations in the chemistry and in the metabolism of such lipids brought about by various factors, such as age, diet, pathological conditions and hormonal influences are being studied. The chemical and biochemical observations are supplemented with histological studies of the tissues.